The use of x-ray diffraction techniques for measuring residual stresses in crystalline substances such as metal or ceramic materials is well-known. The general idea with the use of x-ray diffraction is to subject the material to the radiation of x-rays with the resulting sensed x-ray diffraction peak interpreted to arrive at a measurement of a strength related characteristic, i.e. stress, retained austenite, hardness of the part material, to show, for instance, the level of fatigue in the material. While using coupons or removing the part from service for measurement by x-ray diffraction laboratory equipment is done, neither is particularly satisfactory in that coupons require a portion of the part to be removed therefrom, and removing a part to be measured from service can create undue downtime along with the requisite labor for removal and replacement of the part back into service.
Accordingly, there is a need for portable x-ray diffraction equipment that can be used in the field at the site at which a part is located and without requiring the part to be removed from service. Portable x-ray diffraction equipment is known, however, some of these units suffer from great bulk making them less than ideal for use in field conditions. A further shortcoming with known x-ray diffraction equipment lies in the limitations in moving the goniometer head so that measurements can be taken across a sufficient number of positions on the part to obtain meaningful information therefrom, particularly where the part being tested has been used in the field where corrosion and other environmental use conditions can cause highly localized variations in the strength characteristic being determined. When the only measurements taken are those including such localized aberrations, the determination of what the remaining useful life of the part is before it needs to be retired to avoid fatigue failure thereof can be compromised.
In the laboratory setting this shortcoming requires periodic operator intervention to shift the part being measured so that the goniometer head is in position to direct x-rays at different positions thereon. As is apparent, such operator intervention is time consuming and labor intensive. In the field with current portable units, an operator generally has to physically shift the x-ray diffraction unit including the goniometer head along the part to the different positions at which measurements are desired. In either instance, there is significant operator intervention that is required which is undesirable. In addition, a portable x-ray diffraction unit is needed that can take measurements from complexly-shaped parts and preferably without having to remove them from service while also providing an easy to interpret readout of the results of the measurements to show variations in the fatigue of the part in the region thereof that is measured.
In this regard, currently there is no means available to directly and quantitatively measure the total strain and hence be able to calculate the total stress non-destructively, the dead load strain and hence the dead load stress on the following: wire rope and/or single strand and/or multi-strand cables once they are installed on a structure or component. In addition there is no technique which can determine the strains on individual strands which may comprise a cable bundle or wire rope.
It would be desirable to be able to measure the total strain and hence determine the total stress on these types of load bearing members. Total strain is the residual strain plus the restraint strain plus the applied strain. Accordingly, the total strain relates to a material's remaining capacity to bear a load which is information that is particularly useful for load bearing structures for a number of safety and economic reasons.
Similarly, it would be desirable to be able to measure the dead load strain and hence dead load stress, which is the strain as a result of the weight and restraint stain of the structure or component without the strain due to the intended carrying load.
Another problem is that currently there is no means available to directly, accurately and non-destructively track the changes in wire rope and cable strain due to corrosion, creep, fatigue, overload etc.
A further problem is that currently there is no means available to directly and quantitatively and non-destructively measure the strain and hence be able to calculate the stress on the following: wire rope and or single strand and or multi-strand cables installed on an existing structure or component.
Despite the widespread use of cables, there are few tools available to inspect and characterize the stresses on cables. In fact, at this time there are two techniques currently in common use, a direct measurement by “jacking”, literally by deflecting the cable with a calibrated jack and an indirect method using the “time to damping” of an induced vibration. Both of these approaches to stress measurement are at best an approximation of cable force due to underlying assumptions as discussed in F. A. Zahn and B. Bitterli's paper “Developments in Non-Destructive Stay Cable Inspection Methods” delivered at the IABSE Symposium in San Francisco in August, 1995 (see pp. 861-866). This is because the accuracy of the measurement is less than ideal, the total stress in the cable is ignored and the techniques cannot characterize individual strands which may comprise a cable bundle. Accordingly, there is a need for an apparatus and method that can address these shortcomings.